The present invention relates to a disk discrimination method for a digital versatile disk (DVD) system.
A larger amount of information can be recorded on a DVD than a compact disk (CD), and a better quality of picture can be reproduced therefrom, which may be a next-generation information media.
A DVD system for reproducing signals from a DVD mostly includes a DVD/CD combination optical pickup, so that it can reproduce signals from a CD having a relatively smaller track pitch as well as the DVD. The DVD system having a DVD/CD combination optical pickup should discriminate whether a disk is a DVD or CD before signals are reproduced from the disk. An admitted prior art technology for discriminating whether a disk is a DVD or CD is disclosed in Korean Patent Application 96-1605 filed by Samsung Electronics Co., Itd.
FIG. 1 is a flow-chart diagram showing a DVD/CD discrimination method disclosed in the above Korean Patent Application, which relates to a method which is adapted in a DVD system adopting a DVD/CD combination optical pickup which is provided with a ring-shaped shielding film. As is well known, the thickness of a CD is about 1.2 mm and that of a DVD is about 0.6 mm. When information is read from a relatively thin DVD, light in a near-axial region and a far-axial region reaches a photodiode. Meanwhile, when information is read from a relatively thick CD, only near-axial light reaches the photodiode. The amount of light detected from the DVD becomes more than that detected from the CD.
If an optical disk is loaded (step 110), the DVD system swings a focusing actuator up and down (step 120). During the time when the focusing actuator is swung up and down, if a focus error signal Sf according to the amount of light reaching a divided-by-four split photodiode is larger than a first reference value corresponding to a DVD as shown in FIG. 2A (step 130), the DVD system judges that a loaded disk is a DVD. Meanwhile, if a focus error signal Sf is smaller than the first reference signal as shown in FIG. 2B and larger than a second reference value corresponding to a CD (step 140), the DVD system judges that the loaded disk is a CD. If it is judged that the focus error signal Sf is smaller than the second reference value, an error message indicating that disk discrimination fails is output from the DVD system.
The method disclosed in the above prior art application discriminates the thickness of a disk only once using only one of a sum signal and a focus error signal of the amount of light. Accordingly, reliability of discrimination is lowered at the place where an initial position of an object lens is locally and severely damaged in the disk or a smaller signal is detected than the second reference value. Also, such a disk discrimination is not performed properly even when an offset of a detection signal fluctuates.